Semiconductor workpieces are often implanted with dopant species to create a desired conductivity. For example, solar cells may be implanted with a dopant species to create an emitter region. This implant may be done using a variety of different mechanisms.
In certain embodiments, an ion source is used. In certain embodiments, the ion source may comprise an RF ion source. This RF ion source may include an RF antenna, to which RF power is applied. The RF antenna may be disposed near a wall of the ion source chamber, which may be made of a dielectric material. One or more gas containers may be in communication with the ion source chamber so as to supply feed gas to the ion source chamber. The excitation of the RF antenna results in the creation of electromagnetic energy, which may excite feed gas disposed within the ion source chamber to create a plasma. Ions from this plasma may be extracted from the RF ion source using, for example, extraction electrodes, and directed toward a workpiece. These extracted ions may become implanted in the workpiece.
In other embodiments, the ion source may include an indirectly heated cathode, which emits energetic electrons. These electrodes collide energetically with the feed gas in the ion source chamber, forming ions, which may be extracted through an extraction aperture. Of course, other ion sources may also be used.
In certain embodiments, it may be beneficial to create a high current ion beam. In certain embodiments, this may be done by creating a denser plasma in the ion source. In the case of an RF ion source, this may be achieved by increasing the RF power supplied to the RF antenna and/or supplying more feed gas to the ion source chamber. However, increased consumption of feed gas may increase the overall cost. Additionally, higher RF power may result in elevated contamination levels and lower dopant fractionation. High RF power may also result in a shortened life for the RF ion source and therefore, lower tool utilization.
Therefore, an apparatus that increases ion beam current for an ion source without these drawbacks would be beneficial. It would be advantageous if the apparatus created a high density plasma near the extraction aperture to maximize the extracted ion beam current.